1. Field of the Invention
This invention relates to a high speed method and apparatus for making pouches, bags and the like.
2. History of the Related Art
Presently in the packaging industry pouches and bags are made on conventional machines by heat sealing side seams and bottom seams or glue sealing these seams. In the heat sealing machines which are presently in wide use, electrically heated heater bars shaped to the pattern of the seal to be made are pressed into physical contact against the webs which are to be sealed with a production output limiting dwell time being required for conduction of heat through the webs to their sealing interface to effect a seal.
In the glue sealing machines which are widely used in industry and which are manufactured by a large number of different machine makers, glues suitable for paper, film or foil are applied in patterns for the side seams and bottom closure.
Production outputs are limited by the mechanical applicator's maximum frequency and the "green-tack" time for the glue to "bite" and hold the glue interfaces together before the bags are delivered from the bag machine and pressure packed in bundles allowing the glue to slowly lose its solvent or aqueous components and permanently set.
The average output in bags per minute ranges from 60 to 200 in the case of the heat seal machines and from 100 to 1000 per minute in the glue seal machines. The norms are 125 and 200 per minute, respectively. All of these machines require mechanical set-up time for change of bag size with various change of size parts. With some square bottom bag machines, a series of machine sizes are made to cover the range of bag sizes due to the mechanical complexity of parts and adjustments being too great to be accommodated in one machine.
In the heat seal machines extensible heat sensitive thermoplastic webs such as polyethylene film present limitations in the type of construction for the pouch or bag due to the heat weakening of the web by a 1/8" to 1/2" wide heat seals across the web at right angles to web motion. This allows only "side-weld" bags to be made or necessitates web transport means to support the "jelly-like" condition of the transverse seal area until it cools and recovers sufficient tensile strength to resist the normal machine operating web tension.
The majority of bags and pouches printed today such as cookie bags, dog food bags, cake mix and crystal pouches, etc., have high quality graphics usually in rotogravure printing. This necesitates the pouch and bag making to be a separate operation from the printing operation. The "print-and-make" bag making in-line operations are usually in the relatively lower quality flexographic printing and limited to the lower web speed of bag making which is in the order of 100 to 200 feet per minute vs 600 to 1000 feet per minute in modern flexographic and rotogravure presses. Also modern flexographic and rotogravure press widths usually allow the pouch or bag web to be printed two, three, four or more wide and slit into single roll widths for the pouch or bag machine. This increases the printing output six to ten times that of the in-line "print-and-make" bag method, provides superior quality half tone printing and the viable economics of one $2,000,000 rotogravure press output matching the total output of three or four $300,000 pouch or bag machines. The first printed bags, where the printing was held in register on the bag face or to the bag machine cut-off, were by necessity produced with a tail end printer in line with the bag machine (print-and-make method) and driven by a "one-time-side-drive-shaft" from the bag machine i.e. one revolution of the printing cyclinder or printing impression per one cut-off of the bag machine. The printed repeat or impression length was pre-selected to exactly match the bag machine cut-off length and register variations caused by web tension changes were manually controlled by the operator adjusting a compensating web roll situated between the tail end printer and the bag machine which would lengthen or shorten the web path between the printer and bag machine causing the print to arrive at the cut-off knife later or sooner respectively and thus move down or up to register to the bag cut off line. This method is slow and waste is high both related to the skill of the operator in watching the printed web and making the correct compensator roll adjustment at the right moment and in the right amount.
A great improvement occurred in the 1930's with the development of electronic register control for bag machines allowing the compensator roll to be automatically adjusted, or the bag machine pull rolls through a differential drive to be automatically slowed down or speeded up while in continuous motion. This development also allowed preprinted off line webs to be made into pouches and bags keeping the printing in register to the pouch or bag face and to the cut off knife cut line. The control being photo cell activated by a web "lay-mark" usually a small black rectangle about 1/8" wide in machine direction by 1/2" long across machine direction which was pre-printed on the web, usually at the edge of the web or in the area of the bottom closure folds to be hidden from sight in the final bag, in an off line printing operation. This development improved the printing quality on bags, reduced waste and allowed printed bags to be made at increased speeds previously limited by operator skill and human error. However, the pouch and bag machine speeds are still limited by the inherent frequency limitations of mechanical moving parts, particularly opening and closing mechanisms for the application of adhesive glues or heater jaw actuation for seal patterns and areas in thermo-sealed seams and closures. The majority of heat seal pouch and bag machines have time consuming intermittent web motion or a series of mechanical heat sealing stations to provide sealer bar web contact dwell time in the order of 0.50 second to allow heat transfer from the high temperature sealer bar surface through the web to the sealing interface. Also, considerable bag machine down time, skilled labour and waste is encountered at each "set up" of a glue or heat seal machine for a pouch or bag of different size to be made within the limited size range of each machine. Also, expensive change of size parts are often required for each pouch or bag size the machine is to produce. With the steadily rising costs of new and physically improved pouch and bag materials in papers, films and foils, increasing labour rates and capital cost of pouch and bag machines the packaging industry in this area is operating at 1950 outputs, unit costs and qualities in the 1980 higher quality and efficiency demanding market place.
The use of adhesives to overcome the above limitations of heat sealing in the manufacture of pouches or bags from single wall heat sensitive thin thermoplastic films such as polyethylene or substrates with the thermoplastic coatings is counter productive because the barrier qualities of the films or coatings prevent the rapid escape of the solvent or aqueous components of the adhesives necessary to effect a high speed strong seal.